Condensed Consolidated Statements of Changes in Equity - USD ($) shares in Millions, $ in Millions	Total	Ordinary shares	Additional paid-in capital	Retained earnings	Accumulated other comprehensive loss
Beginning Balance at Dec. 31, 2016	$ 4,254.4	$ 1.8	$ 2,920.8	$ 2,068.1	$ (736.3)
Beginning Balance (in shares) at Dec. 31, 2016		181.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	87.8			87.8
Other comprehensive income, net of tax	77.3				77.3
Dividends declared	(64.0)			(64.0)
Exercise of options, net of shares tendered for payment	9.5		9.5
Exercise of options, net of shares tendered for payment (in shares)		0.2
Issuance of restricted shares, net of cancellations (in shares)		0.3
Issuance of restricted shares, net of cancellations	0.1	$ 0.1
Shares surrendered by employees to pay taxes	(6.7)		(6.7)
Shares surrendered by employees to pay taxes (in shares)		(0.1)
Share-based compensation	16.4		16.4
Ending Balance (in shares) at Mar. 31, 2017		182.2
Ending Balance at Mar. 31, 2017	4,374.8	$ 1.9	2,940.0	2,091.9	(659.0)
Beginning Balance at Dec. 31, 2017	5,037.8	$ 1.8	2,797.7	2,481.7	(243.4)
Beginning Balance (in shares) at Dec. 31, 2017		180.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	102.9
Other comprehensive income, net of tax	(1.4)				(1.4)
Dividends declared	(62.6)			(62.6)
Stock Repurchased During Period, Value	(150.0)		(150.0)
Stock Repurchased During Period, Shares		(2.2)
Exercise of options, net of shares tendered for payment	5.8		5.8
Exercise of options, net of shares tendered for payment (in shares)		0.1
Issuance of restricted shares, net of cancellations (in shares)		0.3
Issuance of restricted shares, net of cancellations	0.0	$ 0.0
Shares surrendered by employees to pay taxes	(4.8)		(4.8)
Shares surrendered by employees to pay taxes (in shares)		(0.1)
Share-based compensation	6.0		6.0
Ending Balance (in shares) at Mar. 31, 2018		178.4
Ending Balance at Mar. 31, 2018	4,719.7	$ 1.8	$ 2,654.7	2,308.0	$ (244.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting changes	$ (214.0)			$ (214.0)